Iron-based amorphous alloy ribbons exhibit excellent soft magnetic properties including low magnetic loss under AC excitation, finding their applications in energy-efficient magnetic devices such as transformers, motors, generators, etc. In these devices, ferromagnetic materials with high saturation magnetization and thermal stability with small core loss and exciting power are preferred. Fe—B—Si-based amorphous alloys meet these requirements. However, higher saturation magnetization is required for these amorphous alloys to reduce the size of transformers, etc.
U.S. Pat. No. 6,471,789 discloses a metal alloy strip having a composition represented by the formula of FeaBbSic, wherein a, b and c are atomic percentages ranging from about 79 to less than 80, greater than 10 and up to 16, and 5 to 10, respectively, with the sum of a, b, and c being 100, and b being greater than c, the alloy strip having a core loss of less than about 0.22 W/kg at 60 Hz and an induction value within 1.0-1.5 Tesla, and the alloy having effective amounts of boron and silicon such that the strip is at least singularly ductile and is at least 75% in an amorphous phase. Though this metal alloy strip has high magnetic induction with small core loss and exciting power, our research has revealed that when bent with a small radius of curvature to form transformers, it likely has large internal stress, which cannot sufficiently be removed even by a heat treatment, resulting in a relatively large core loss and exciting power.
JP 9-143640 A discloses a wide, amorphous alloy ribbon used for power transformer cores having a composition represented by the chemical formula of FeaBbSicCd, wherein a, b, c and d are numbers (atomic %) meeting 78.5≤a≤81, 9.5≤b≤13, 8≤c≤12.5, and 0.4≤d≤1.5, the ribbon being cast in an atmosphere containing 40% or more by volume of a carbon dioxide gas by a single-roll, liquid-quenching method, the as-cast ribbon having a width of 70 mm or more, and a roll-contacting surface of the as-cast ribbon having a centerline-averaged roughness Ra of 0.7 μm or less. JP 9-143640 A describes that this wide, amorphous alloy ribbon has excellent magnetic properties, thermal stability, workability, and productivity, suitable for power transformer cores.
However, because 8-12.5 atomic % of Si is contained in this wide, amorphous alloy ribbon of JP 9-143640 A, it has been found that relatively large internal stress remains in a core formed by laminating and bending this amorphous alloy ribbon, even after a heat treatment. In addition, though FIGS. 1-9 in JP 9-143640 A show wider ranges of Fe, B, Si and C than those recited in the claims, the specification of JP 9-143640 A exhibits only examples of Fe—B—Si—C amorphous alloys with 79 atomic % of Fe. The chemical compositions specifically shown in JP 9-143640 A are limited to Fe79B11.5Si9C0.5 (FIG. 1), Fe79B10.5Si10.5-XCX (FIGS. 2-4), Fe79B20.5-ySiyC0.5 (FIG. 5), FeZB10.5Si89-ZC0.5 (FIGS. 6 and 7), and Fe79B20.5-ySiyC0.5 (FIGS. 8 and 9). Thus, the amount of Fe is limited to 79 atomic % when the amount of Si is 9 atomic % (FIG. 1), when the amount of C is changed from 2 atomic % to 5 atomic % (FIGS. 2-4), when the amount of Si is changed from 6 atomic % to 12 atomic % (FIG. 5), or when the amount of Si is changed from 8 atomic % to 14 atomic % (FIGS. 8 and 9), and the amount of B is limited to 10.5 atomic % when the amount of Fe is changed from 77 atomic % to 83 atomic % (FIGS. 6 and 7).
US 2012/0062351 A1 discloses a ferromagnetic, amorphous alloy ribbon having a composition represented by FeaSibBcCd, wherein 80.5≤a≤83 atomic %, 0.5≤b≤6 atomic %, 12≤c≤16.5 atomic %, 0.01≤d≤1 atomic %, with a+b+c+d=100, and incidental impurities; the alloy ribbon being cast from a molten alloy with a surface tension of greater than or equal to 1.1 N/m on a chill body surface; the ribbon having protrusions on the surface facing the chill body surface; the protrusions being measured in terms of height and their number; the protrusion height exceeding 3 μm and less than four times the ribbon thickness; and the number of protrusions being less than 10 within 1.5 in of the ribbon length; and the ribbon in its annealed straight strip form having a saturation magnetic induction exceeding 1.60 T and exhibiting a magnetic core loss of less than 0.14 W/kg when measured at 60 Hz and at 1.3 T induction level. However, our research has revealed that a transformer core formed by laminating and bending this ferromagnetic, amorphous alloy ribbon with a small radius of curvature likely has large internal stress, which cannot sufficiently be removed even by a heat treatment.
WO 2013/137118 A1 discloses an amorphous alloy ribbon comprising Fe, Si, B, C and inevitable impurities; the amount of Si being 8.5-9.5 atomic %, and the amount of B being 10.0-12.0 atomic %, when the total amount of Fe, Si and B is 100 atomic %; the amount of C being 0.2-0.6 atomic %, per 100 atomic % of the total amount of Fe, Si and B; the ribbon having a thickness of 10-40 μm, and a width of 100-300 mm. WO 2013/137118 A1 describes that this amorphous alloy ribbon has a high space factor and magnetic flux density with suppressed brittleness. However, our research has revealed that a transformer core formed by laminating and bending this amorphous alloy ribbon with a small radius of curvature likely has large internal stress, which cannot sufficiently be removed even by a heat treatment.